Vagueness

When you are vague, the listener feels the
tension of uncertain meaning and will usually
add in their own detail rather
than exist with the uncertainty. This can be undesirable when you want to be
clear and precise but it can be very useful when you want them to put themselves
into a frame or otherwise engage in meaning-making.

Vagueness can also be deliberately
used to provoke conversation as it
effectively requires the other person to ask for
clarification.

Ambiguity

Vagueness happens when what is said can be interpreted in different ways.
This may happen when the words used can have multiple meanings.

Are you set? Can you go?

Omission

A way of being vague is to leave out details of
who, what, when, how much, and so on. When something is incomplete then it may
be assigned multiple meanings or may just be uncertain about what the real
meaning is.

Well, you know what they say, it often takes time and effort.

Classification

Understanding something requires classifying it into some type or another.
Vague classification avoids completely putting the item into a single category.
This may be done using broad categories that allow for a lot of internal
variation or using a classification that itself is rather vague.

It was a small mammal of some sort.

I'm an expert.

Uncertainty

By showing that you are not certain about what you are describing then you
cast everything said into doubt. This also lets you off the hook for being
responsible for an absolute definition. If people later say 'you said', you can
reply 'well, I did say I wasn't quite sure'.

I'm not completely sure, but I think it was a dog.

It's almost certainly a dog.

Uncertainty can also be linked with a limited memory. If you cannot remember
then you cannot be certain.

It had floppy ears, as I remember.

Approximation

When an estimate is made, then the other person may still have to guess.
Approximations can be quite accurate or may be extremely vague. Approximation is
signified by words like almost, about, roughly, around, most, etc.

About a hundred people came. I'd say almost everyone I know
was there. There were less than fifty left after four o'clock.

Persuasively, an approximation acts as an
anchor
which will tend to keep further estimation, thought and discussion around this
anchor point.

Probability

Probability and possibility get into the realms of statistics and
forecasting. This may be indicated by words such as likely, perhaps,
maybe, seems, etc.

It seems likely that she might come.

Whilst this does not assure that something is true or will happen, it has the
persuasive benefit of making people think about what might be and hence increase
their assessment of whether something is indeed possible or likely. The
Availability
Heuristic also means that when something is talked about then it will come
to mind more easily and is assessed as being more likely.